This invention relates to a pressure vessel, and, more particularly, to a modular containment system for removing and replacing a cover of a pressure vessel. This invention is particularly applicable to removing and replacing bottom covers of coke drums.
The processing of crude oil into gasoline, diesel fuel, lubricants, and the like, as well as many other petroleum-refining operations, produces byproducts that have very little value. However, the value of these byproducts can be substantially increased when they are heated for a long enough time at a temperature sufficient to cause what is known as xe2x80x9cdestructive distillation.xe2x80x9d During the process of destructive distillation, a portion of the byproducts is converted to usable hydrocarbon products. The remainder is transformed into a solid carbon product called xe2x80x9ccoke.xe2x80x9d The temperature at which destructive distillation normally occurs is about 900 degrees F. Generally, an industrial furnace is used to incur destructive distillation.
Conventionally, a large pressure vessel known as a coke drum is provided at a furnace outlet for a sufficient amount of time to allow for a complete destructive distillation reaction. A typical coke drum is a large, vertical metal vessel with top and bottom closures. The actual size, shape, and configuration of the coke drum, however, can vary considerably from one installation to another. The bottom closure typically includes a relatively large and heavy removable cover that is secured to the drum by dozens of bolts. Disengagement and reengagement of the removable cover, known as unheading and heading, respectively, can be quite labor intensive, given the mass of the cover and the numerous bolts that hold it in place.
During the refining process, petroleum byproducts are deposited in the coke drum as a hot liquid slurry. Typically, the slurry enters the drum through an opening in the bottom closure. Lighter hydrocarbons, the products of destructive distillation, flow out the top of the coke drum while heavier material remains inside the drum.
After a coke drum is filled to the desired capacity and the flow of slurry into the drum ceases, the drum is cooled. This typically involves injecting steam into the drum to strip useful hydrocarbon vapors from the solid material and then injecting water into the drum to further cool the coke. The liquid mass remaining in the coke drum is substantially full of coke that, as it cools, hardens into solid material. This solid coke must be removed from the drum before the drum can be reused. The process of removing coke from a drum is referred to as xe2x80x9cdecoking.xe2x80x9d
A typical decoking process involves several steps. First, any water remaining in the drum is drained through piping to allow for removal of the cover from the bottom closure of the drum. In a hydraulic operation, as opposed to a manual operation, the cover is supported by a hydraulic lifting mechanism to detension the joint. Next, the cover must be unlocked from the coke drum and disengaged in a controlled manner by manipulating the bolts attaching the cover to a flange on the drum. The cover then is lowered by the hydraulic mechanism. As can be appreciated, unheading a coke drum can be a time consuming process. After unheading is complete, the coke in the drum is cut out of the drum by high pressure water jets. The operation is reversed to resecure the cover on the drum.
To help streamline the unheading process, oil refineries frequently use automated unheading devices. Such unheading devices typically are provided at the lower end of the coking drums for automatic and semi-automatic heading and unheading and are capable of being remotely operated. An example of a known remotely operated unheading device for a coking drum is disclosed in U.S. Pat. No. 4,726,109 to Malsbury et al. In that patent, a platform device is provided beneath the coking drum for lowering the header unit (or cover), moving the header unit laterally to one side, and tipping it to facilitate cleaning of the header unit.
Other examples of remotely-operated removable closures are shown in U.S. Pat. Nos. 4,820,384, 5,290,072, and 5,221,019. For example, in the ""384 patent a remotely-operated vessel cover assembly includes a cover which can be attached to a flange surrounding an opening-in the vessel. When the cover is raised into position, a series of connector pins fits through corresponding holes in a force ring and keyhole-shaped holes in a lock ring. The lock ring then is rotated so that heads of the connector pins are locked behind the lock ring. Fluid pressure then is applied to a force actuator, pressurizing inner and outer annular rings, which expand to pre-stress the pins and the cover. A ramp ring then is rotated until a series of ramps thereon firmly contacts a complementary series of ramps on the cover. The force actuator is then depressurized. According to this patent, the angle of inclination of the ramps is sufficiently shallow that friction between the ramp ring and the cover prevents slippage.
Automatic and semi-automatic unheading devices that confine the flow of discharge from the drum to a storage arrangement by means of a chute are also known in the art. For example, U.S. Pat. No. 6,039,844 to Malik discloses a containment system for coke drums including a safety shield, a removable cover, a plurality of actuators, and a system to vertically position the shield. The Malik patent also discloses an inner shield telescopically disposed within the safety shield to channel discharge from the coke drum to a switch deck floor.
Despite the current state of the art, there is a need in the art for a system that reliably contains and controls the entire unheading and heading process. There is a further need for such a system that is conducive to remote actuation. There is a still further need for such a system that is modular in construction so as to be easily transported and removably disposed around the bottom closure of a coke drum. There is also a need in the art for a system that confines drum discharge when the cover is disengaged from the flange and simplifies the process of delivering the discharge to an unheading deck floor.
Accordingly, it is a principal object of the present invention to provide an improved unheading and containment system for a pressure vessel.
According to one aspect of the present invention, an unheading and containment system is provided having an unheading apparatus for removing a cover from a pressure vessel in an unheading operation, and a modular enclosure mechanism. The unheading apparatus includes a cover removably secured to the pressure vessel, a lock plate that cooperates with the cover, and a cover moving mechanism capable of moving the cover vertically and laterally. The modular enclosure mechanism includes a chassis that substantially encloses the cover during the unheading operation. The unheading apparatus may also include a flange mounted to a headed end of the pressure vessel and having a plurality of fasteners cooperating with the lock plate to secure the cover to the pressure vessel when the cover is brought into aligned contact with the flange.
According to another aspect of the present invention, a pressure vessel unheading and containment system is provided having a removable cover closing a pressure vessel bottom outlet and a chassis substantially enclosing an area between the bottom outlet and a support surface, with the cover contained within the enclosed area in an open position and a closed position. The system may also include a flange mounted to the pressure vessel at the bottom outlet and a lock plate cooperatively connected to the cover. The flange and the lock plate cooperate to secure the cover to the bottom outlet.
According to yet another aspect of the present invention, a pressure vessel unheading and containment system is provided having an unheading means for unheading a cover from a bottom outlet of the pressure vessel and an enclosure means for substantially enclosing the unheading operation performed by said unheading means. The system may also include a cover moving means adapted to move the cover vertically and laterally.
The unheading means may comprise a removable cover, a lock plate cooperating with the cover, and a cover moving mechanism capable of moving the cover vertically. The system may also include a flange mounted to the pressure vessel near its bottom outlet and having a plurality of fasteners cooperating with the lock plate to secure the cover to the pressure vessel.